This invention relates to propellant binders and more specifically to an energetic binder composition useful in solid, composite-modified single and double base propellants, and a process for the preparation of such propellants.
Present day composite type propellants ordinarily consist of one or more solid inorganic or organic oxidizers uniformally distributed in particulate form throughout a matrix of an energetic plastic, resinous or elastomeric binder material, such as nitrocellulose, which serves as the fuel component for the combustion reaction. Depending upon whether the propellant contains a single combustible material, such as nitrocellulose, or a mixture of more than one combustible material, such as nitrocellulose admixed with nitroglycerin, the propellant is classified as either single or double base.
Solid composite propellants are generally prepared by mixing the solid particulate oxidizer with a resinous or elastomeric liquid matrix, and solidfying the composition after a uniform dispersion of the solid is obtained. According to previous studies, improved mechanical properties such as superior creep life, tensile strength and elongation, are obtained by chemically cross-linking the matrix either prior to or subsequent to solidification. Such improved mechanical properties are highly desirable in preventing alteration of burning characteristics due to internal cracking of the propellant grain either during processing or as a result of the high localized stresses generated during rocket flight.
Prior attempts to cross-link nitrocellulose-containing propellants, however, have been largely unsuccessful due mainly to the absence of a suitable cross-linking agent. Common cross-linking agents, such as the isocyanates, are generally unsatisfactory due to their tendency to react with residual moisture which generates carbon dioxide and creates internal voids within the propellant grain. Unless the matrix material is rigorously dried prior to cross-linking, formation of voids may result in serious weakening of mechanical and ballistic properties. Relatively large voids, in fact, tend to result in severe malfunctioning of the motor.